1. Field of the Invention
The present invention relates to systems for arresting movement of large bodies and, more particularly, to a method and apparatus for alleviating the initial high impact force of a moving vehicle or aircraft against a capturing means.
2. Description of the Prior Art
External devices for stopping the high velocity movement of large bodies within a short distance are generally described with reference to aircraft landing arrestment devices. U.S. Pat. No. 3,876,170 describes the use of a complicated net arrangement deployed across the landing path of an aircraft. Major and minor groupings of Nylon nets are slung between stanchions on opposing sides of the landing area. The ends of the nets are connected to known energy absorption mechanisms such as hydraulic arrestor gears. The nets successively break-away from the stanchions as an incoming plane engages the various groupings. The plane is finally halted with the energy absorption apparatus.
Other patents like Canadian Pat. No. 807,033 and Belgium Pat. No. 657,843 are concerned with improvements on the energy absorption apparatus per se. Such apparatus are connected to the ends of a strap or cable which is stretched across a landing strip. As the aircraft lands, a hook engages the strap or cable to bring the craft to a halt.
The Canadian patent particularly describes an elongated prismatic box that inhibits tangling of the strap at the entrance of the energy absorption apparatus. The Belgium patent concerns a multiple hydraulic piston arrangement connected to the cable ends through flared tubes for absorbing the inertial energy of a landing aircraft.
In those systems utilizing taut cables or the like for engagement with a hook mechanism, pronounced transverse waves are propagated along the cable span. These waves radiate outward from the hook impact point. They continue until interrupted by some external means associated with the cable. When interrupted, the wave is reflected back toward the aircraft hook. At the same time the wave is reflected back, another tensile-load increase is generated in the cable at the point of reflection. The many tensile-load increases generated each time a wave is reflected back along the cable span accumulate rapidly and would cause the cable to fail if the tensile-load increases were not absorbed by the energy absorption devices.
British Pat. No. 1,081,537 has recognized the desirability of dampening the initial transverse wave to alleviate rapid tensile-load increases. The patentees attach a second cable to the main cable for attachment of various types of dampening means. These include heavy weights, springs and a hydraulic brake. Alternatively, the main cable is split into two cables with each terminating in a braking device. In such case, four braking devices are required for the overall system.
It is clear that the system described in the British patent is cumbersome and requires a great deal of space and equipment. Further, the amount of transverse wave reflection would be very difficult to regulate due to all the variables implicit in the different dampening techniques.